3.1 Squads are your units - the most important part of the game. Choosing the right squad makes the difference between survival and death. It is best to specialize in one squad type and then have a lesser amount of proficiency with several other types.

3.2 To use squads, you need books and tomes. Books are the major ones - they have wider categories, but are rarer and furthermore you can't even use a unit unless you have their book. Tomes are more about specifics; these can be found or bought from the merchant, and tend to cover certain styles related to the main book. For example, "swords" is a book. However, "sword and shield", "two-handed sword", and "dual sword" are all tomes.

3.3 Using a squad enough will level them up. Levels give you proficiency points which can be used in two category types. The first of these is a general increase - stats like attack, defense, speed, and number of troops. These apply to all squads covered by the book. The second is to increase particular special attacks, which applies only to units covered by a specific tome.

3.4 As mentioned before, it is best to specialize in one squad type, but have other squad proficiencies available if the need arises. Since there will be many times where the only units you have access to are generic soldiers from a friendly army, it helps if you have a wide range of units that you are okay with in case your specific preferred unit isn't present.

3.5 The other important part of having multiple unit types available is the range of weaknesses and strengths that each unit has. Relying on a single unit type will get you killed if you encounter units that are stronger than you and have the advantage, so unless you always travel with a column of allies it is good to have some backup plans.

3.6 Mercenaries are purchased at the tavern, and can be summoned in battle. Only units for which you have both the book AND the tome can be commanded, and the actual specific unit tends to vary. To check a unit's power, look at their weapon; they're almost always the same as your own weapon levels (as in, weapons that you can buy) so judge what you know about weapons to judge power levels. For example, "Greatsword" soldiers carry claymores, while Landsknechts carry flamberges. Looking at our inventory screen, we can see that flamberges are more powerful than claymores, and this is reflected in the soldiers themselves. The only time this hasn't been true is with halberdiers - I do better with the regular soldiers than with the supposedly more advanced "South China Spears", but this is mostly because that weapon has much less range than most halberds.

3.7 As a side note, you can summon mercenaries and then not take command of them; they will help you with whatever battle you are currently fighting, but will not go anywhere afterwards. Also, they spawn at whatever level everyone else on the battle is, and also tend to die fairly easily. However, they are pretty useful if you're outmatched in a fight.

3.8 One last point: the armor and weapons you buy only apply to you. The armor is on all the time, but the weapons only show up when you switch to a squad of that type. So, don't feel obligated to buy weapons for squads you don't intend to use. Bladestorm the Hundred Years War Walkthrough